A complete description of an inkjet printer and an inkjet print cartridge is provided in U.S. Pat. No. 5,648,806, entitled "Stable Substrate Structure For A Wide Swath Nozzle Array In A High Resolution Inkjet Printer," by Steven Steinfield et al., assigned to the present assignee and incorporated herein by reference. In inkjet print cartridges, poor print and image quality can be caused by misplaced ink drops, referred to as dot placement error or DPE. A main contributor to DPE is nozzle camber angle (NCA) caused by warpage of the tape automated bonded (TAB) head assembly. The TAB head assembly is a strip of flexible tape having nozzles formed therein and conductors formed on its back surface. A printhead substrate is secured to the back of the tape, and electrodes on the substrate are connected to the conductors on the tape. Contact pads on the cartridge receive electrical signals from the printer to eject ink drops from the nozzles.
The tape is secured to the snout of the print cartridge, and a fluid seal is made between the tape and the body of the print cartridge to allow ink to be fed around the edges of the substrate (or through a hole in the substrate) in order to reach ink ejection chambers formed on the top of the substrate. An ink ejection element in each ink ejection chamber is energized to eject a droplet of ink through an associated nozzle located over each ink ejection chamber.
A great deal of the flexible tape warpage may be created during the assembly process of securing the TAB head assembly to the print cartridge body.
Besides warpage affecting the nozzle angles, other undesireable effects caused by non-flatness of the TAB head assembly include die edge camber angle and macrodimple. These defects affect print quality, print speed, reliability, and serviceability. The table below summarizes the different components of the TAB head assembly flatness and their effects on customer perceivable attributes of the end product.
The flatness component of causes affecting NCA Drop trajectory print quality (Nozzle camber angle) variation throughput: (directionality) (# of printmode passes required) DECA Drop volume and drop print quality (Die edge camber angle) velocity variation DECA Firing chamber refill print speed (Die edge camber angle) frequency variation/reduction Buckling (a.k.a. Wiping and capping serviceability "macrodimple")/Warp (a.k.a. margin reduction "ripple") Buckling (a.k.a. Delamination stress, ink reliability "macrodimple")/Warp (a.k.a. shorts robustness "ripple") degradation
FIG. 1 is a perspective view of an inkjet print cartridge 10, and FIG. 2 is a cross-sectional view of the printhead portion of the print cartridge of FIG. 1 along line 2--2. The components in the above table are identified in FIG. 2.
Generally, print cartridge 10 of FIG. 1 includes a print cartridge body 12, having a snout 14, which typically faces downwards toward a medium when the cartridge is installed in a scanning carriage. A printhead area 16 includes a nozzle member 18 having nozzles 20 formed therein. Nozzle member 18 may be formed of a flexible tape 22 (FIG. 2), as described above, or may be any other thin material.
Below nozzle member 18 is a printhead substrate 24 (FIG. 2), typically formed of silicon, having formed on it ink ejection elements, an ink ejection chamber surrounding each ink ejection element, and ink channels leading to the ink ejection chambers. Details are described in U.S. Pat. No. 5,648,806.
FIG. 2 is a cross-section along line 2--2 of FIG. 1 illustrating one type of printhead using a TAB head assembly. The plastic print cartridge body 12 supports the edges of the TAB head assembly. A substrate 24 is shown attached to the underside of the flexible tape 22. Ink flows from a reservoir in the print cartridge body 12 (or from an external reservoir) through an ink channel 25 in the print cartridge and into ink channels formed in a barrier layer on the surface of the substrate 24. The flexible tape 22 is sealed with respect to the print cartridge by an adhesive 26. Energizing signals are coupled to copper traces 28 formed on the back of the flexible tape 22 to energize the ink ejection elements to eject droplets of ink from the nozzles 20 formed in the flexible tape 22. A cover layer 30 prevents ink from contacting the copper traces 28.
As seen from FIG. 2, the flexible tape 22 is warped, which results in the effects previously described. One cause of the warpage is due to the thermal cycling of the print cartridge during manufacturing. The coefficients of thermal expansion of the print cartridge body 12 and the flexible tape 22 are not the same, causing the two components to expand to different extents when being heated, such as during heat curing of the adhesive 26. When these components are later cooled to room temperature, the fixing of the tape 22 to the print cartridge body 12 by the adhesive 26 causes compression of the tape 22 and distortion.
What is needed is a technique for improving the flatness of the TAB head assembly or any other nozzle member assembly.